To be honest, the pricing is pretty much in keeping with the norm.
If you buy 500 leaflets you pay more than someone who buys 10,000 pro-rata, its the same for window cleaning. A house with a lot of windows generally will be discounted down and to be honest the owners are not stupid and will be looking for this.
Like i have said before, you have to look at the benefits this type of work brings, stability (they don't generally move about) It gives you an edge on new business (Name drop that you clean this manor etc....) and the fact that they will recommend you to thier friends, who will also live in reasonable size houses too? Word of mouth is so valuable.
Trev